1. Field of the Invention
The present invention relates to a drive apparatus for driving a gas injection nozzle for a plastic molding die apparatus. The die apparatus has a die that is movable with an external operation and is preferably, for example, a plastic molding die apparatus adaptable to gas injection molding to form a hollow portion in a molded product.
2. Description of the Prior Art
A conventional gas injection molding method uses a gas injection nozzle for introducing gas into resin enclosed in a die cavity space.
The injection molding apparatus disclosed in Japanese Patent Appln. Laid-Open No. 64-14012 has a reciprocating gas injection nozzle.
FIG. 6 is a cross sectional view of the foregoing injection molding apparatus. FIG. 7 is an enlarged cross sectional view of the gas injection nozzle of the foregoing conventional structure.
Referring to FIGS. 6 and 7, reference numerals 210 and 214 respectively represent upper and lower platens, and 211 and 212 represent upper and lower dies. Reference numerals 213 and 216 represent surfaces of the upper and the lower dies 211 and 212 respectively. Reference numeral 219 represents resin injected into the cavity, and 225 represents a space formed in a molded product after the gas has been injected.
The foregoing apparatus includes a single-shaft fluid cylinder 227, disposed adjacent to lower die 212, to move a gas injection nozzle 226 having a center hole 228 therein. As shown in FIG. 7, gas injection nozzle 226 has a cap portion 232 at a leading portion thereof. A ball is inserted into cap portion 232, forming a check valve 230. Gas injection nozzle 226 is directly connected to a piston 229 of the fluid cylinder 227. The fluid cylinder 227 is secured to the lower die 212. Therefore, to inspect cap portion 232, for example for maintenance, the fluid cylinder 227 must be removed. Since a gas supply pipe 238 is positioned outside the fluid cylinder 227, as shown in FIG. 6, a space for the piping and wiring must be created by cutting the die 212.
If the fluid cylinder 227 is fastened adjacent to the lower die 212 as described above, a die fastening plate 251, an ejector plate and an ejector pin (omitted from the illustration) must be removed to attach/detach the gas injection nozzle 226. Therefore, the attachment and detachment of the gas injector nozzle can require excessive time and labor.
Further, the fluid cylinder 227, adjacent to the lower die 212, is located at an intermediate position between the die ejector and the product cavity. Thus, it is difficult to design and locate the ejector pins, required to eject a molded product, for the area in which the fluid cylinder is located.